Advantages obtained from continuous casting of metal sheets with counter-rotating rollers and electromagnetic confinement of the molten metal at the edge of the rollers are described in U.S. Pat. Nos. 4,936,374 and 5,385,201. These patents are parent applications of the present application, were granted to the inventor of the present invention, and are assigned to the same entity as this application.
A combination of mechanical and electromagnetic means to contain molten metal at the edges of counter-rotating rollers is described in U.S. Pat. Nos. 4,936,374 and 5,385,201. Methods are described in these patents to achieve low reluctance at the edges, or rim portions, of the counter-rotating rollers for horizontal alternating magnetic flux which confines the molten metal between the rim portions of the rollers. These methods range from extending the rollers with solid stainless steel rims to cutting slots into the roller rims and filling the slots with refractory material, stainless steel or ferromagnetic laminations. Other methods described use laminated hoops for the roller extension or hoop-shaped magnet pole assemblies contained inside rims which are welded to the rollers.
All of the above methods have drawbacks for certain practical applications. Saw-cut slots are typically .gtoreq.0.8 mm (0.031") wide. High temperature slot-fillers cause an uneven roller-rim-surface and reduce the thermal conductivity and mechanical strength of the roller rim edge. The slot-filler, whether refractory material, stainless steel or a combination of metal and adhesive, is exposed to thermal expansion due to the molten metal and to deformation due to roller pressure once every roller revolution. This will deteriorate the slot-filler and cause consequential deformation of the surface of the edge of the steel-strip being cast.
Because slotted low reluctance rims add complexity to the roller design of twin-roller-casters utilizing horizontal alternating magnetic fields for sidewall containment, twin-roller-casters have typically used solid roller rims. It was erroneously assumed that twin-roller-caster-rollers could easily absorb the eddy current losses in their rims and that cooling of the edges of the cast metal-sheet would not be adversely affected by the eddy current losses in the roller rims. Recent experiments with solid rollers have shown that eddy current losses in the roller rims produce red-hot temperatures therein. This reduces the roller rims' ability to cool and solidify the sheet being cast at the edge of the roller in comparison with the much cooler center portion of the rollers which are not exposed to eddy currents. This phenomenon often prevents the cast metal sheet from solidifying satisfactorily at the edges. In addition, the large eddy current losses in the roller rims substantially increase the power requirements and magnet costs for electromagnetic sidewall containment of molten metal.
Accordingly, it is an object of the present invention to provide a novel apparatus and method for preventing a pool of molten metal from flowing over the ends of counter-rotating rollers, comprising a shaped horizontal alternating magnetic field and low reluctance rims for the rollers to reduce eddy current losses in the rim portion of the rollers when casting metal sheets.
It is still another object of the present invention to provide a novel apparatus and method for preventing a pool of molten metal from flowing over the ends of counter-rotating rollers, comprising a shaped horizontal alternating magnetic field and low reluctance rims being part of the rim or edge portion of rollers otherwise made from one solid metal.
It is still another object of the present invention to provide a novel apparatus and method for preventing a pool of molten metal from flowing over the ends of counter-rotating rollers, comprising a shaped horizontal alternating magnetic field and low reluctance rims being part of rollers having multilayer construction of different metals.
It is a further object of the present invention to provide an improved method and apparatus for preventing a pool of molten metal flowing over the ends of counter-rotating rollers, comprising a shaped horizontal alternating magnetic field and low reluctance rims with ferromagnetic inserts to reduce roller-rim-losses, to force a more uniform field distribution in the low reluctance rims and to reduce the magnetomotive force required for the containment field.
It is a still further object of the present invention to provide an improved method and apparatus for preventing molten metal from flowing over the ends of solid or multilayer counter-rotating rollers, comprising low reluctance rims which are attached to the sidewalls of the rollers of a caster.
It is a further object of the invention to provide a novel method and apparatus that contains electromagnetically molten metal between counter-rotating rollers with a minimum of power dissipation in the edges (rims) of the rollers.
It is still a further object of the invention to provide an improved method and apparatus that contains a pool of molten metal from flowing out sides of a containment means with a minimum of electrical power consumed by the containment means.
The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with the further objects and advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings, wherein like reference numerals identify like elements.